1. Field of the Invention
The present invention relates generally to the encryption and decryption of data. More particularly, the present invention relates to the encryption and decryption of data streams.
2. Background Art
Today, digital content is typically transmitted from one location to another using a transport stream, such as an MPEG-2 transport stream. Once received, the transport stream can be decoded into suitable audio and video signals, which can be used by an output device to view the content. As such, content providers typically encrypt the transport stream prior to transmission to prevent unauthorized parties, i.e., non-subscribers, from receiving and viewing the content without having paid for it. Consequently, content providers are continuously striving for more impenetrable and highly robust encryption methods for protecting their content.
FIG. 1 shows a transport stream that is encrypted using a conventional encryption method. As shown in FIG. 1, encrypted transport stream 102 has encrypted portions 104, 106, 108, and 110, where each encrypted portion includes a sequence of encrypted transport packets. As also shown in FIG. 1, encrypted portions 104, 106, and 108, and 110, are defined by encryption intervals 112, 114, 116, and 118, respectively. As further shown in FIG. 1, encrypted portion 104 is encrypted with “Algorithm 1” utilizing “Odd Key 1,” encrypted portion 106 is encrypted with “Algorithm 1” utilizing “Even Key 1,” encrypted portion 108 is encrypted with “Algorithm 1” utilizing “Odd Key 2,” and encrypted portion 110 is encrypted with “Algorithm 1” utilizing “Even Key 2.” For example, Algorithm 1 can be a Single Data Encryption Algorithm (SDEA), a Triple Data Encryption Algorithm (TDEA), a Common Scrambling Algorithm (CSA) such as that used in the Digital Video Broadcasting (DVB) system, or an Advanced Encryption Standard (AES) Algorithm.
Thus, as shown in FIG. 1, the key e.g., Odd Key 1, is changed every ten seconds, such that each encryption interval e.g., encryption intervals 112, 114, 116, and 118, spans a period of ten seconds. For example, as shown in FIG. 1, Odd Key 1 is used to encrypt the transport stream for the first ten seconds, e.g., during encryption interval 112, while Even Key 1 is used to encrypt the transport stream for the subsequent ten seconds, e.g., during encryption interval 114. By periodically changing the key used by Algorithm 1, the conventional encryption method used to encrypt the transport stream increases the difficulty of unauthorized decryption of the encrypted transport stream. The conventional encryption method used in FIG. 1, however suffers a critical weakness because if the algorithm used to encrypt the transport stream, i.e., Algorithm 1, is hacked by a third party, then the encrypted transport stream can be easily decrypted, thereby allowing the content to be freely viewed.
Thus, there is a strong need in the art for a method and system for encrypting and decrypting a data stream.